As a light source used for a projection-type display such as a projector, a solid-state light source having a long life and a wide color gamut has been attracting attention. In recent years, a light source unit that utilizes light emitted from a phosphor by irradiating the phosphor with light of a solid-state light source has been used for a projector, etc.
The above-described light source unit includes, for example, a phosphor layer, and a solid-state light source that irradiates the phosphor layer with exciting light. For light emission of the phosphor layer, there is a phenomenon called luminance saturation or temperature quenching. This is such a phenomenon that, in a case where an output of the exciting light is increased, a part of a conversion loss in the phosphor layer changes to heat that causes the phosphor layer to generate heat, and fluorescence conversion efficiency thereby drops. In a state where the fluorescence conversion efficiency is low, an efficient, bright light source unit is not implementable. Hence, the phosphor layer is provided on a surface of a substrate having high thermal conductivity.